Add util function to get value from arg

This is a more advanced version meant to eventually replace the
`_get_arg_values` in decorators.py.

1 files changed, 34 insertions, 0 deletions

diff --git a/bot/utils/function.py b/bot/utils/function.py
new file mode 100644
index 000000000..7c5949122
--- /dev/null
+++ b/bot/utils/function.py
@@ -0,0 +1,34 @@
+"""Utilities for interaction with functions."""
+
+import typing as t
+
+Argument = t.Union[int, str]
+
+
+def get_arg_value(name_or_pos: Argument, arguments: t.OrderedDict[str, t.Any]) -> t.Any:
+    """
+    Return a value from `arguments` based on a name or position.
+
+    `arguments` is an ordered mapping of parameter names to argument values.
+
+    Raise TypeError if `name_or_pos` isn't a str or int.
+    Raise ValueError if `name_or_pos` does not match any argument.
+    """
+    if isinstance(name_or_pos, int):
+        # Convert arguments to a tuple to make them indexable.
+        arg_values = tuple(arguments.items())
+        arg_pos = name_or_pos
+
+        try:
+            name, value = arg_values[arg_pos]
+            return value
+        except IndexError:
+            raise ValueError(f"Argument position {arg_pos} is out of bounds.")
+    elif isinstance(name_or_pos, str):
+        arg_name = name_or_pos
+        try:
+            return arguments[arg_name]
+        except KeyError:
+            raise ValueError(f"Argument {arg_name!r} doesn't exist.")
+    else:
+        raise TypeError("'arg' must either be an int (positional index) or a str (keyword).")